Analyzing the hazards that accompany large earthquakes requires an understanding of the interplay between the long term motion of tectonic plates and the structural features near active faults. As tectonic plates move and deform, faults (or cracks) between and embedded in the plates do not slide but are locked due to frictional resistance. As time passes (tens to hundreds of years for large earthquakes) the stress on these faults increases. An earthquake rupture occurs when the level of stress resolved on the fault exceeds the frictional resistance (at least in some local region of the fault). Thus modeling the full earthquake cycle (tectonic loading, nucleation, and full evolution of rupture) is challenging because it requires the resolution of many vastly different timescales. Additional challenges arise from the fact that faults are geometrically complex -- with large-scale bends and branches as well as small-scale non-planar features -- and are surrounded by heterogeneous materials including sediments and clays, as well as much stiffer materials such as granite. Furthermore, field observations of faults reveal an abundance of cracks and micro-fractures -- often referred to as a damage zone -- which must often be included in models to produce realistic results. In this project we will develop, validate, and utilize an earthquake cycle model that can rigorously and self-consistently handle complex fault geometries, damage zones, and heterogeneous materials. We will also explore how geometry and heterogeneity affect the earthquake locations, magnitudes, and recurrence intervals. This proposed work benefits the society at large as understanding the impact of complexity on the earthquake cycle directly informs our understanding of seismic hazard.

Seismic hazard analysis requires an understanding of the earthquake cycle including the interaction of remote loading and near-fault structure. Currently, no existing models can account for both the interseismic and coseismic periods with complex fault geometries, heterogeneous materials, and plastic deformation. This funding supports the development and application of a numerical model that rigorously accounts for interseismic loading as well as rupture dynamics in both two- and three-dimensions. To capture the effect of slow tectonic loading on the evolution of the stress field, a computationally efficient quasi-static model will be used. As inertial effects become important, the model will transition to a fully dynamic description where the wavefield is modeled along with its interaction with fault interfaces. All stages of the earthquake cycle will be modeled in a single, self-consistent computational and mathematical framework capable of capturing both complex geometries and material descriptions. The group will develop a parallel quasi-static and dynamic rupture modeling environment that handles complex geometries (e.g., branches, bends, and step-overs), general boundary conditions, plastic deformation, and variable material and frictional properties. The investigators will use the developed model to consider how geometry affects nucleation location, recurrence interval, magnitude, and evolution of the near-fault stress field will be studied as well as the role that plasticity and bi-material properties play when all stages of the earthquake cycle are rigorously considered.

National Science Foundation (NSF)
Division of Earth Sciences (EAR)
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Paul Raterron
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Portland State University
United States
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